Cellulosic fibrous structures are commonly found in many consumer products. Cellulosic fibrous structures, such as toilet tissue, facial tissue and paper towels are a staple of daily life. Toilet tissue, facial tissue and paper towels are used throughout home and industry for a variety of purposes.
Several features of toilet tissue, facial tissue and paper towel consumer products are desired by, if not important to, the consumer. For example, the consumer frequently desires a cellulosic fibrous structure in the form of one of the aforementioned consumer products which has a relatively high caliper. The relatively high caliper imparts the appearance of strength and of a durable, high quality consumer product. Technically, a relatively greater caliper may favorably affect the appearance, cleaning ability, tactile impression and absorbency of the cellulosic fibrous structure.
The caliper of a cellulosic fibrous structure may be increased according to a variety of methods known in the prior art. For example, the basis weight of the cellulosic fibrous structure may be increased, so that more cellulosic fibers are present per unit area. However, this method has several drawbacks. Particularly, a uniform distribution of a relatively larger quantity of the cellulosic fibers may not be the most efficient utilization of raw materials and, in fact may even represent a waste of, rather than merely poor economization of, the raw materials. Also, there now exists a current and growing emphasis on economizing renewable resources such as cellulosic pulp. Utilizing more fibers per unit area of a consumer product such as toilet tissue, facial tissue or paper towels is contrary to this growing public demand.
One way to overcome the aforementioned disadvantages of increasing caliper by simply increasing the basis weight of the cellulosic fibrous structure and still achieve an increase in caliper is to utilize a multi-ply structure. For example, U.S. Pat. No. 3,940,529 issued Feb. 24, 1976 to Hepford et al. discloses a sheet having two webs, each with crests and depressions. The crests and depressions of each web are registered so that the crests of each web are positioned between the crests of the other web, yet spaced from the depressions. The webs are joined at locations intermediate such crests and depressions. This arrangement provides an increase in caliper over that obtained by simply joining two otherwise like webs of equivalent basis weight but not having crests and depressions. This increase is due to the void space intermediate the webs. However, this teaching requires careful positioning, arranging, and registering of the crests and depressions of each sheet so that the two webs are properly joined.
Similarly, commonly assigned U.S. Pat. No. 4,100,017 issued Jul. 11, 1978 to Flautt, Jr. discloses multi-ply tissue products having dissimilar webs. In this teaching a low density, high bulk web is united with a conventional web. This arrangement results in a laminate that is thicker and softer than that obtained by joining two identical webs. However, manufacturing complexity is increased by having dissimilar materials to stock and supply vis-a-vis utilizing the same materials throughout the multi-ply tissue product.
U.S. Pat. No. 4,320,162 issued Mar. 16, 1982 to Schulz and U.S. Pat. No. 4,376,671 issued Mar. 15, 1983 to Schulz disclose multi-ply sheets. Each ply is joined to the opposite ply at deep spot embossments. Between the deep spot embossments each ply has shallow secondary embossments which are offset from the shallow secondary embossments of the other ply. Both the deep and shallow embossments are oriented towards the center of the multi-ply sheet. These teachings suffer from the drawbacks that the deep and shallow embossments are inwardly oriented. If the embossments were oriented outwardly, and away from the center of the sheet, an increase in apparent caliper might possibly result, because the apexes of the embossments would be spaced further apart. Similarly, U.S. Pat. No. 3,556,907 issued Jan. 17, 1971 to Nystrand discloses an embossed laminate having two laminae with offset projecting embossments oriented towards the center of the laminate.
An enhancement of the teachings is found in U.S. Pat. No. 4,921,034 issued May 1, 1990 to Burgess et al. Burgess et al. discloses paper having up and down bosses formed across the mid-plane of the web. Each boss is asymmetric, with the up bosses having a different X-Y orientation than that of the down bosses.
However, the Hepford et al., Flautt, Jr., both Schulz, Nystrand, and Burgess et al. teachings suffer from the drawback that multiple ply consumer products are more complex, and hence more expensive to manufacture. Multiple ply products require an extra converting operation to join the two (or more) plies and additional warehousing and handling of matched parent rolls so that the resulting product does not consist of mismatched or incompatible plies.
One attempt involving single ply products which has been very commercially successful in overcoming certain disadvantages of the prior art is to utilize the drying section of the papermaking machine to enhance properties, such as caliper, of consumer products. Particularly, blow-through drying of the cellulosic fibrous structure--rather than press felt drying--can increase the caliper of the cellulosic fibrous structure. Blow-through drying may, at the same time, increase the tensile strength and burst strength of the cellulosic fibrous structure. Examples of consumer products made in this manner are illustrated in commonly assigned U.S. Pat. No. 4,637,859 issued Jan. 20, 1987 to Trokhan.
Another manner in which relatively high caliper may be attained without uneconomical use of the materials is by utilizing the forming section of the papermaking machine used to manufacture the cellulosic fibrous structure. For example, as illustrated in commonly assigned U.S. Pat. No. 4,514,345 issued Apr. 30, 1985 to Johnson et al., a forming belt having protuberances which displace a certain volume of the cellulosic fibers may be utilized. However, the resulting consumer product may have limited opacity in the regions where the fibers are displaced by the protuberances. Thus, using the same quantity of cellulosic fibers may result in a higher caliper, lower opacity consumer product vis-a-vis a constant basis weight cellulosic fibrous structure.
Yet another well known way to increase the caliper of cellulosic fibrous structures is by mechanical embossing. In fact, mechanically embossed patterns are very common in cellulosic fibrous structures, and considerable efforts in the prior art have been directed to mechanically embossing cellulosic fibrous structures. As used herein, mechanical embossing refers to the application of force to the cellulosic fibrous structure through rigid members, such as protrusions on the periphery of rolls. One well known mechanically embossed pattern which appears in paper towel consumer products marketed by The Procter & Gamble Company, the assignee of the present invention, is illustrated in commonly assigned U.S. Pat. Des. No. 239,137 issued Mar. 9, 1976 to Appleman.
Mechanical embossing may be performed by either of two well known processes, nested embossing or knob-to-knob embossing. Nested embossing utilizes protrusions and depressions in axially synchronously rotated embossing rolls. This produces a like pattern of protrusions and depressions in the cellulosic fibrous structures produced thereby, as illustrated in U.S. Pat. No. 3,556,907 issued Jan. 19, 1971 to Nystrand and in U.S. Pat. No. 3,867,225 issued Feb. 18, 1975 to Nystrand.
In knob-to-knob embossing the protrusions of the mechanical embossing rolls are registered, producing a cellulosic fibrous structure having discrete sites in each of two laminae bonded together. Knob-to-knob embossing is illustrated in commonly assigned U.S. Pat. No. 3,414,459 issued Dec. 3, 1968 to Wells.
Either of these two mechanical embossing processes will produce one or more sites or regions of the cellulosic fibrous structure which is out of the plane of the balance or the background of the cellulosic fibrous structure. By having sites or regions of the cellulosic fibrous structure displaced from the plane of the balance or background of the cellulosic fibrous structure, differences in elevation, taken perpendicular to the plane of the cellulosic fibrous structure become apparent and the overall caliper is increased. Such increase does not require the utilization of more materials per unit area, because, generally, the basis weight remains generally constant in the embossed and nonembossed sites or regions of the cellulosic fibrous structure.
However, the mechanical embossing processes imparts caliper at the expense of other properties desired by the consumer. Particularly, mechanical embossing disrupts the bonds between fibers resulting in a cellulosic fibrous structure having less tensile strength, and possibly less softness, than existed before the mechanical embossing.
Another feature often desired in consumer products such as toilet tissue, facial tissue and paper towels is a particular surface texture. A surface texture can be functional, such as providing efficacious cleaning or scrubbing. A surface texture may also be aesthetic, imparting a more quilted or cloth-like appearance to the cellulosic fibrous structure.
A particular surface texture may be imparted by mechanical embossing, as discussed above. However, imparting a surface texture by the mechanical embossing processes results in a cellulosic fibrous structure having the aforementioned drawbacks.
Surface texture may also be influenced by having high basis weight and low basis weight regions present within the cellulosic fibrous structure as described relative to the aforementioned Johnson et al. patent. However, not all forming sections of papermaking machines are able to accommodate multiple basis weight cellulosic fibrous structures when manufacturing consumer products.
It is thus apparent that none of the foregoing prior art provides the benefits of this invention. Particularly, none of the prior art known to Applicant teaches a cellulosic fibrous structure which increases caliper and provides a surface texture of a single lamina without mechanical embossing, or joining to another lamina.
Accordingly, it is an object of this invention to provide a method of increasing the caliper and surface texture of a single lamina cellulosic fibrous structure. It is an object of this invention to do so without unduly sacrificing other material properties desired by the consumer. Finally, it is an object of this invention to do so without requiring the cellulosic fibrous structure to be joined to another lamina to form a laminate.